As is generally known, a fingerprint has various features including ridges, valleys, minute points, and the like. The minute points include bifurcations where ridges furcate and end points where ridges end. The fingerprint feature distribution is different for each individual and individuals do not have the same fingerprint, and thus fingerprints are regarded as highly specific biometric data. Therefore, a security system that employs biometric data such as a fingerprint can accurately and effectively secure premises, movable assets, and the like.
The recognition and authentication technology using such fingerprint information is used in various fields due to its superior performance with a simple structure. Especially, it becomes important to effectively distinguish an artificially manufactured fingerprint (hereinafter, referred to as ‘fake fingerprint’) from a human fingerprint, as the technologies have been widely used in fields requiring high security, such as access control, electronic commerce, and financial transactions.
A fake fingerprint may be detected by measuring physiological analyte such as hemoglobin or the like through spectrum distribution characteristics of reflected or scattered light after irradiating a light to a finger to identify a fake fingerprint. Alternatively, a fake fingerprint may be detected based on a change in capacitance which is caused by a finger when the finger approaches a metal plate of a fingerprint sensor prism on which a small amount of charge is formed.
Further, a fake fingerprint may be detected by radiating light from the outside such that light is transmitted through a finger along an inner surface adjacent to a surface of the finger, acquiring a surface image by detecting light passing through the finger, and analyzing the surface image to judge whether or not it is a fake fingerprint. Since the living body has a large degree of light attenuation, the light rapidly attenuates while it proceeds inside of the body, and then disappears. On the other hand, in a fake fingerprint, the degree of light attenuation is small, so that most of the light is transmitted, and there is little difference between an incident light amount and a transmitted light amount. Accordingly, it is possible to identify a fake fingerprint by using the characteristic difference between the finger and the fake fingerprint.
The present applicant has proposed a device and a method for identifying a fake fingerprint in Korean Patent No. 10-1436786. The disclosure of Korean Patent No. 10-1436786 analyzes a correlation between an image produced by an external light source and an image produced by an internal light source, and judges whether a fingerprint is fake. This has the advantage that contains changes in the degree of contact between the fingerprint and a prism depending on the state of the fingerprint is acceptable.
As described above, radiation direction and radiation angle of light radiated by the internal light source are very important in identifying a fake fingerprint using an image by the internal light source and an image by the external light source. This is because the radiation direction and the radiation angle of the light determine the angle or amount of the light reaching the finger or the fake fingerprint and the identifying performance for the fake fingerprint may be varied.